Methods and apparatus for recording write requests directed to a data store

Abstract

A storage management device records write requests that are directed to a data store. In one embodiment, the storage management device records a plurality of write request entries, each one of which includes information relating to a write request, in at least one first database table, and maintains, for each first database table, at least one record in a second database table. The one or more records in the second database table include data representing the effects of the write requests on a state of at least one portion of the data store. In one such embodiment, each time that one write request entry is recorded in one first database table, the storage management device updates at least one record in the second database table.

Description

CROSS REFERENCE TO RELATED APPLICATION [0001] This application is a continuation-in-part of U.S. patent application Ser. No. 10 / 668,833, filed Sep. 23, 2003, the disclosure of which is hereby incorporated herein by reference in its entirety.TECHNICAL FIELD [0002] The present invention relates to data storage. More particularly, the invention relates to methods and apparatus for recording write requests directed to a data store. BACKGROUND [0003] Business enterprises rely increasingly on computer systems that allow the sharing of data across a business enterprise. The data storage systems that have evolved to store large amounts of data typically are critically important to an enterprise. As a result, the disruption or failure of the data storage system can cripple operation of the entire enterprise. [0004] Data used by applications running on computer systems are typically stored on primary storage devices (e.g., disks) and secondary storage devices (e.g., tape and cheaper disk driv...

AI Technical Summary

Benefits of technology

[0012] The present invention addresses the shortcomings of current systems by facilitating the recovery of data at any prior point in time. In particular, the present invention permits data stored in a data store to be recovered, without requiring that a snapshot of the data store be created, at a point in time just prior to the occurrence of a corrupting event.

[0013] Even more particularly, the present invention provides a storage management device that facilitates the storage of data at, and the subsequent recovery of data from, one or more physical stores. The storage management device may be implemented in a network and it may receive data for storage in the physical stores from one or more other devices connected to the network.

[0015] According to one advantage, the storage management device can rapidly and efficiently interpret the data stored in the records of the second database table to determine which particular units of storage have been overwritten. According to another advantage, given a particular past point in time, and charged with the task of generating a time map (i.e., a map that has the current locations of data that was stored in at least one portion of the data store at a specified past point in time), the storage management device can interpret the data stored in the records of the second database table to identify a subset of the first database tables to search for write request entries that are relevant to the generation of the time map. In other words, the storage management device need not search through all first database tables and through all write request entries to generate the time map. Accordingly, overall efficiency is improved, and rapid generation of the time map is made possible.

Problems solved by technology

As a result, the disruption or failure of the data storage system can cripple operation of the entire enterprise.

Information technology departments typically deal with a number of problems concerning data storage systems.

Generally, however, these fall into two broad categories: hardware failure and data corruption.

Thus, if a disk failure occurs, the user still has application data residing on the other mirror disks.

However, mirroring is ineffective when data corruption occurs.

Data corruption comes in many forms, but it generally is recognized when the user's application stops functioning properly as a result of data being written to the disk.

There are many possible sources of data corruption such as a failed attempt to upgrade the application, a user accidentally deleting key information, a rogue user purposely damaging the application data, computer viruses, and the like.

Regardless of the cause, mirroring actually works against the user who has experienced data corruption because mirroring replicates the bad data to all the mirrors simultaneously.

Thus, all copies of the data are corrupted.

Additionally, because the disks are continuously updated, a backup of historical data, i.e., a snapshot of the data present in the data storage device at a past time T, can only be created if the system is instructed to save the backup at or prior to time T. Thus, at time T+1 the system is unable to provide a backup of the data current at time T. Further, each unit of storage is saved regardless of whether the data stored in it is unchanged since the time that the previous backup was made.

Such an approach is inefficient and costly because it increases the storage capacity required to backup the data storage device at multiple points in time.

Also, the mirroring approach becomes less efficient and more error prone when employed with larger data storage systems because large systems span hundreds of disks and the systems cannot assure that each disk is backed up at the same point in time.

Consequently, complex and error prone processes are employed in an attempt to create a concurrent backup for the entire data storage system.

This approach suffers, however, from the same shortcomings as mirroring, that is, all snapshots are created at the then current point in time either in conjunction with the users request or as a result of a previously scheduled instruction to create a snapshot of the stored data.

Also, generation of single point in time images generally is a lengthy process.

Because these solutions are only attempts at fixing existing approaches they do not provide a solution that is workable as the capacity of data storage systems continues to increase.

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